Suppose I am using one App (no other App is active). Now I lock the iPad by simply clicking the lock button or may be I put it in background mode and put my iPad somewhere.
After what amount of time, the App will get killed automatically by system if I don't use that App? Is there any specification by Apple or we cannot say anything that App will launch from scratch in some scenarios.
Note that in any scenario, I don't kill my App manually.
iOS generally (at least in current versions) doesn't kill apps after some arbitrary time. It kills them when it needs to free up resources. Since modern iPads have quite a bit of memory, that means that apps can stay in the background for a very long time depending on how the iPad is used. As Andreas notes, however, there are no promises about that.
Related
It seems like older versions of iOS allowed your app to run for 10 minutes in the background. Now it seems like iOS only allows your app to run for a maximum of 3 minutes. I haven't found any documentation mentioning when, or in which versions, this changed, or any estimates provided by Apple for how long your app can run in the background.
I need to be able to run in the background, because my app is connected to an external device via TCP. I already know about the hacks you can do with VOIP and playing silent audio (both will get your app rejected).
Is there anything I can do to get my app to keep running in the background longer than 3 minutes?
We haven’t had the old 10 minute window for years so that is simply no longer applicable. That was reduced to 3 minutes in OS 7, and further reduced to 30 seconds in iOS 13. (There is a new concept of background tasks, for running tasks longer than 30 seconds, but the the OS will run these at its own discretion, e.g. at night, when the user is charging their device, so that’s not really applicable here).
The short answer to your question is that you cannot submit apps to the store that run in the background indefinitely unless it’s one of a very limited list of permitted background modes.
If you can go to the “Signing & Capabilities” tab of your target and add “Background Modes” and you can see the list of alternatives:
So, with the caveat that you cannot do precisely what you asked, here are a few observations:
The “External accessory communication” background mode (see ExternalAccessory) seems promising, but that’s for bluetooth or wired connections only. So unless you can refactor/reengineer how your devices communicates, that is likely not a viable solution.
There’s an interesting question of whether just keeping the app running in the foreground might be helpful (e.g. judicious use of idleTimerDisabled). I know this solves a different problem (and should be used only where essential), but perhaps it’s option for you.
If your external device is Internet-enabled and you want it to inform the app of some event, perhaps you can have it communicate its intent to some web service that then triggers an APNS push notification that your device can receive.
Bottom line, you can’t do what you ask, but if you edit your question with more details about the nature of the device and what your iOS app wants to do with that device, we might be able to provide better counsel. But in answer to the general question “can I just keep app running perpetually in the background”, the answer is “no.”
Is there any possibility to know which apps are in the background (Those apps that appear when you double tap home button)?
For 3rd party apps, no. Not in a reliable, App Store safe, future proof way. Think of your app as siloed, unaware of what else is running, and you'll be pretty much in the mindset Apple want (and try to technically enforce).
For other apps developed by you, you can use shared containers to write load/unload data each time one of your apps opens/closes, and work out what's currently running.
This is not possible on iOS with public api. There might be private api calls that do this, even though I don't think you will have access to them while running in the sandbox. This however might be possible on jailbroken devices, but you will not be able to submit to the app store with such api usage, unless you know how to hide that from apple.
Also please note that apps shown in the app switcher are not necessarily running. The app switcher shows every app that has been running in the past which the user didn't force-quit. If the user does not force quit an app, every app that has ever been launched is shown in the app switcher. If iOS decides to terminate an app because of memory needs, the app is still shown in the app switcher. This is one of the reasons why everyone should implement state restoration, as the user does not know whether an app is currently running or not!
My app is an emergency app. It will be used by people in emergency and disasters.
It's possible that they got stuck in situations where they just don't have the time to enter or draw their password on the lock screen, launch the app and push a button. Is it possible that my app can ask the OS to launch the app if user throw their iPhone up in the air or shake it vigorously or something else.
What I wish to achieve by this ?
I want that OS launches my app in background if the user say shake his/her iPhone vigorously. Once launched my app will make a network request and keep running in background for short time.
PS:I think it's possible with the accelerometer.
Accelerometer will not work because Apple doesn't allow background processes opening apps. In your case, user must be opening the app by himself/herself manually. (PS. As far as I know, it's possible in Android)
iOS background tasking problems aside:
Apple don't allow apps that encourage the user to do things that might damage their iOS device. So your 'throw in the air' idea is out.
As for shaking the device -- this just isn't practical. What if the device gets shaken by accident? You've then got false alarms to deal with.
The crux of the issue is that something that triggers an emergency response should be a deliberate action which is hard to do trigger by accident.
This cannot work - and here's why.
Your app would need to run in background to handle motion events. Apps running in background can get killed at any time, i.e. if memory gets low. There might be some restrictions about running and and resource usage as well.
An app in the background cannot bring itself to the front.
Launching from a locked screen would bring great security risks.
Throwing into the air seems like a gesture that can easily be triggered by accident.
I must admit that I'm pretty happy that those apps are not allowed on the AppStore - as it would open many doors that I'd like to see kept close.
This is a strange one, I have a need to create an iOS app that runs in the background on an iOS device, but can not be visible on the Home screen of the device. The app may need to show up in Settings to configure a few options, but it mostly needs to run behind the scenes.
I do not need to publish this app on the app store, it is strictly an enterprise app for my company.
Does anyone know how this kind of behavior might be achieved? Configuration profiles? API's? etc?
Edit: Jailbreaking the device is not really an option for us. We have to keep the devices as they are.
Backgrounding
There are several methods to get permanent background execution:
a) Silent audio which is mentioned by JRG-Developer
b) Usage of beginBackgroundTaskWithExpirationHandler + turning location manager on/off (it will reset remaining time to 600 seconds)
Making app invisible
You can use SBAppTags in Info.plist (take a look at this: How to remove app icon programatically from jail broken iPhone app?)
It will make your icon not visible on Home screen.
I've no idea how you can tackle the not be visible on the home screen criteria, but there are certain services that are allowed to be run in the background continuously, notably:
Background Audio (even silent audio)
While this is indeed very hacky, short of jailbreaking the devices, this may be your best bet.
While it's unlikely / very difficult to get past the review process, in the event for some reason you do need to (attempt) to publish this app to the App Store, some apps are even available on the App Store which take advantage of this hack, such as PasteBot.
You should definitely read their write-up here about getting their app's Cut-and-Paste functionality to work while in the background:
http://tapbots.com/blog/pastebot/pastebot-music-in-background
Another out-of-the-box idea, why not use Android devices instead, which do support multitasking?
Two methods:
Jailbreak. A jailbroken iPhone is essentially a Mac and you can use all Mac UNIX programming tricks - spawn a daemon (you can even ask launchd to do that), or something. You can set up enteprise-wise Cydia source. Refer to saurik's website for a walkthrough and set up an experimental server using Ubuntu (which used apt too)
A non-jailbreak way may be possible, but it will depend on what your app is doing. You can try use enterprise-wise push notifications.
Given that this is impossible to do on non jailbroken phones, I'd suggest the following:
develop a directory app, or a phone list app, something that is specific to your company.
have it connect to a web service once a day to register the device ID (so you know the user has not deleted the app)
tell users they need to keep the app open at all times (and if a user's device does not register one day, send them an email asking them to launch the app).
Now you can send back whatever you want with the app. If they kill it, you'll know the next day when you have a script look at the logs.
If you think this is a terrible idea, it is, but its the best you are going to get on iOS right now.
EDIT: you could send a notification every day - say in the AM - to make sure the user opened the app if it wasn't running.
From my experince, this kind of behaviour cannot be achieved on iOS. When an app enters into background, it is active only for a small particular amount of time. After that, it goes into hybernate state. It stops working. So the behaviour you said can not be achieved without abusing iOS workflow. Thats why some call iOS's multitasking as not true multitasking. Only jailbreaking might help your case. That was for one case. The second one where the app cannot be seen on home screen is again, impossible. It has to be on springboard to run.
I am rather confused about how this would be possible with the iOS Sandbox, but there appears to be an app in the App Store that does this: Dual Core System Activity Monitor for iPhone 4S
According to the Developer Website this app can:
Stop Apps:
Use the Stop Apps button to quickly free up memory. Tap the button and dismiss the dialog multiple times to free up additional memory each time. You do not actually need to double press the Home button to kill the apps.
I am able to get a list of processes running with their pid's. How could I "free up memory" by, I assume, killing processes or other apps?
Note: While I intend to submit this particular project for the App Store, I would still be interested to know how this is done on a jailbroken phone, if that's your specialty. Plus I'm sure other programmers reading this could benefit from such knowledge as well.
I think that's a scam app ..it's iOS's duty to terminate processes if you need more memory.
You could read the list of processes and then virtually terminate them (remove them from a table view or something) but not actually terminate the process itself.
Maybe it is claiming a lot of memory (be still below the threshold) so that iOS kills of other running apps. While shortly after releasing the memory.